Ground-based measurements of NO_x and total reactive oxidized nitrogen (NO_y) at Sable Island, Nova Scotia, during the NARE 1993 summer intensive

Measurements of NO, NO₂, and total reactive oxidized nitrogen (NO_y) were added to ongoing measurements of aerosols, CO, and O₃ at Sable Island (43°55′N, 60°01′W), Nova Scotia, during the North Atlantic Regional Experiment (NARE) 1993 summer intensive. Ambient levels of NO_x and NO_y were found to be highly variable, and elevated levels can be attributed to the transport of polluted continental air or presumably to relatively fresh emissions from sources upwind (e.g., ship traffic). The median values for NO_x and NO_y are 98 and 266 parts per trillion by volume (pptv), respectively. A multiday pollution episode occurred during which elevated NO_x and NO_y were observed with enhanced levels of O₃, CO, and condensation nuclei. Air masses of recent tropical marine origin characterized by low and constant levels of O₃ and CO were sampled after Hurricane Emily. The correlation between ozone and CO is reasonably good, although the relation is driven by the single pollution episode observed during the study. The correlation of O₃ with NO_y and with NO_y-NO_x is complicated by the presumed NO_y removal processes in the marine boundary layer. Examination of the radiosonde data and comparisons of the surface data with those obtained on the overflying aircraft provide clear indications of vertical stratification above the site.